Automatic volume control



Sept. 14, 1937. H0, PETERSON 2,093,095

I AUTOMATIC VOLUME CONTROL Original Filed Feb. 9, 1935 *6N INVENTOR.

H. c. PETERSON www ATTORNEY.

Patented Sept. 14, 1937 UNITED STATES PATENT OFFICE AUTOMATIC VOLUMECONTROL of Delaware Application February 9, 1935, Serial No. 5,734Renewed September 22, 1936 5 Claims.

This invention relates to radio receiving systems and more particularlyto a method of and means for automatically controlling the volume orintensity of received signals at a uniform level.

It is well known, in receivers, to use time constant circuits comprisedof resistance and capacity to control the speed of operation ofautomatic volume control devices. In general, these time constantcircuits function to control the bias applied to the grid of an electrondischarge device after the lapse of an interval approximately anywherebetween one-fifth and ten seconds. If the signal fades slowly down to alow value of intensity, the automatic volume control action through thetime constant circuit operates to compensate the loss of signalintensity by changing the bias on the grid and thus increasing the gainof the receiver so as to maintain a constant output level. On the otherhand, any sudden increase in signal intensity will cause the automaticvolume control device to decrease the gain of the receiver in order tomaintain the same constant output level. A diculty which arises in sucharrangements occurs when signal fading becomes fairly rapid, at whichtime there are experienced sudden abnormally high bursts of outputvolume in the interval immediately succeeding deep fading of the signal.This difliculty is due to the fact that the time constant circuitoperates at a slower rate than the rate at which the signal increases instrength after fading; in other words, the gain in the receiver is notcompensated fast enough to maintain constant output level and the outputmay temporarily be at a very high and abnormal value until the automaticvolume control acting through the time constant circuit succeeds inreducing the gain to the proper value.

The present invention overcomes the above mentioned difficulty andprovides a system wherein the speed of operation of the automatic volumecontrol device is momentarily increased when the strength of theincoming signal suddenly increases.

A feature of the present invention lies in the use of a momentarilyoperative electron discharge device in shunt to a' resistance in thetime. constant circuit. The device is responsive only to sudden largeincreases in voltage across the resistance so as to provide a path oflow impedance through which the capacity of the time constant circuitcan be rapidly charged to a value sucient to restore the output level tonormal.

Referring to the drawing, Fig. 1 illustrates diagrammatically a receiverembodying one form of the invention, and Figs. 2 and 3 illustratemodifications of the automatic volume control circuit of Fig. 1.

The receiving system of Fig. 1 is of the double detection orsuper-heterodyne type in which an intermediate frequency carrier wave isproduced (Cl. Z-20) quency amplier l, the output product of which isdelivered to the negatively biased grid of the second stage of4detection 8. In well known manner, the signal waves impressed ondetector 8 cause plate current to be drawn through resistance I3 and themodulation frequency to appear on the grid of amplifier I4 which ampliesthe low frequency currents and supplies the amplified current to thesignal reproducer I5,-herein illustrated as a loudspeaker.

The current through resistance I3, caused by the signal waves impressedon the input of detecv tor 8, produces a voltage drop which istransferred through'resistance 9.of the time constant circuit to chargecondenser I0 thereof, whereby point. IS assumes a negative value. 'Ihegrid of radio frequency amplifier 3 is connected tothis point whichsupplies the grid bias for automatically controlling the volume of thesystem. It will be apparent that more current will ilow throughresistances 9 and I3, and that point I6 will be more negative asstronger signals are received, in consequence of which the negative gridbias is increased and the gain'in amplifier 3 decreased, thus tending tokeep the plate current through resistance I3 at a constant value. The

time constant of the automatic volume control feature is determined bythe size of resistance 9 and condenser I0.

In accordance with the present invention, there is provided in shunt ofresistance 9, an electron discharge device II comprising cathode II andanode I2 enclosed within an envelope which may be either evacuated orfilled with gas or Vapor.

The characteristic of electronic device I1 is such that as the voltagebetween anode and cathode is increased, the impedance of the pathbetween I2 and II is decreased. Consequently when the signal strengthsuddenly increases after a prolonged period at a low value, the suddenincrease of voltage across resistor I3 engenders a sudden abnormallylarge voltage across resistor 9, upon the occurrence of which the pathbetween electrodes I2 and II of device I'I becomes of low impedance andenables condenser I0 to charge rapidly to a value sufciently negative toquickly restore the normal output level. In this Way the interval ofabnormal output may be reduced to such a short interval as to beunobjectionable.

Although the AVC lead from condenser I0 is shown connected to the gridof the first stage of amplication, it will be understood, of course,that this showing is merely by way of illustration and that this leadmay, if desired, connect with the grids of other stages as well, alsothe automatic control units may be connected to the output of otherstages than detector 8.

Fig. 2 is a modification of Fig. 1 and for the sake of simplicity merelyillustrates the pertinent details of the automatic control featurealone. Vacuum tube 8 herein represents any rectifier in the systemsituated in such part of the circuit that the rectified voltage amountsto several volts. The operation of this circuit is quite similar to thatof Fig. l, with the advantage that a certain amount of vflexibility isprovided by the additional voltage dividing circuit I3, I9. In thesystem of Fig. 2, the automatic control time constant circuit 9, I0derives its voltage from the voltage drop in resistance I3, which istransferred to condenser III through resistance 9. The time constanthere also is determined by resistance 9 and condenser I0. Similarautomatic volume controlling voltage is simultaneously produced acrossresistance I9 and the ratio between resistances I8 and I9 may beadjusted so that p the voltage drop in resistance I9 may be greater orless than the voltage drop in resistance I3. Any sudden increase inamplitude in the output of electron discharge device 8 will appearacross resistance I9 and will produce a path of low impedance betweenelectrodes II and I2, thus immediately charging condenser I0 throughdevice I1.

If desired, a xed value of potential may be inserted in series withdevice I'I to give a required operating condition.

Figure 3 shows a further modification illustrating the use of a diode 20as a rectifier instead of a grid type of rectifier.

It should be understood that the invention is not limited to the precisearrangement of parts shown, since various other forms of shuntingelectron discharge devices, such as mercury rectifier tubes, ordinaryvacuum tubes, and grid controlled glow tubes, known by the trade-nameThyratron, may be employed.

What is claimed is:

1. In a receiving system, an amplier adapted to amplify the incomingwaves, means for rectifying the products of said amplifier, a timeconstant circuit including a resistance and a condenser in circuit withsaid means for impressing a potential obtained from said rectified Wavesupon said amplifier to control its e'ciency, and an electron dischargedevice in shunt with said resistance and responsive to a sudden largeincrease in the intensity of the incoming waves for providing a path oflow impedance across said resistance, whereby said condenser is morerapidly charged to increase the speed of control over said amplifier.

2. In a wave receiver, an automatic volume control system including atime constant element for controlling the degree of amplication of saidreceiver in an inverse manner as the amplitude of the received wavesvaries, an electron discharge device of the diode type in shunt withsaid element and responsive only to sudden large changes in amplitudefor increasing the speed of operation of said control system, and meansincluding a diode detectoradapted to be fed with amplied energy fromsaid receiver for impressing a variable control potential across saidtime constant element and across said discharge device which is in shunttherewith.

3. In a wave receiving system of the type in which an incoming carrierwave is first amplified and then demodulated with a locally generatedheterodyne wave to produce a beat wave of a different frequency, arectifying device for rectifying the beat waves, a resistance in circuitwith the output of said rectifying device across which are produced themodulations of said incoming carrier wave, a translator coupled to saidresistance, a series circuit of another resistance and a condenserconnected between a point on said first resistance and ground, wherebysaid condenser is charged in accordance with the variations inmodulation appearing across said rst resistance, a connection from thejunction point of said condenser and its series coupled resistance to anelement in said system for automatically controlling the degree ofamplification of said system, and a two electrode electron dischargedevice in shunt with said last resistance and responsive to apredetermined sudden ncrease in amplitude of the rectified waves toproduce a path of low impedance across said last resistance, whereby thecharge on said condenser can morerapidly follow the variations inmodulation appearing across said first resistance.

4. In a radio receiving system, an incoming signal wave amplifier, meansincluding a gridcontrolled electron discharge device for rectifying theproducts of said amplifier, means including an impedance circuit betweentwo output electrodes of said grid-controlled electron discharge devicefor deriving potentials which vary with the magnitude of the rectifiedwaves, means including a time constant circuit having a resistorconnected at one end to an intermediate point on said impedance circuit,and at the other end to a point on the input circuit of said amplifierfor controlling the efficiency of said amplier, a capacitor connected tothe last mentioned end of said resistor and in circuit with the cathodeof said electron discharge device, and an electron discharge device ofthe diode type in shunt with said resistor.

5. vIn a signal reception system, a signal transmission tube, adetection tube including an impedance in its space current path acrosswhich is developed a direct current voltage varying in .I

magnitude with signal intensity variation, an automatic gain controlconnection between a gain control electrode of the transmission tube anda point on the impedance which becomes more negative with signalintensity increase, a

resistive element included in said control connection, a device ofuni-directional conductivity in shunt with the resistive element, and aterminal of the said device being connected to said point whereby thedevice becomes conductive and causes current to flow through theresistive element when said point suddenly assumes a highly negativepotential.

HAROLD O. PETERSON.

